Helena Hänninen

Recording locations in multichannel magnetocardiography and body surface potential mapping sensitive for regional exercise-induced myocardial ischemia.

Introduction This study aimed to identify the optimal locations in multichannel magnetocardiography (MCG) and body surface potential mapping (BSPM) to detect exercise-induced myocardial ischemia. Methods We studied 17 healthy controls and 24 coronary artery disease (CAD) patients with stenosis in one of the main coronary artery branches: left anterior descending (LAD) in 11 patients, right (RCA) in 7 patients, and left circumflex (LCX) in 6 patients. MCG and BSPM signals were recorded during a supine bicycle stress test. The capability of a recording location to separate the groups was quantified by subtracting the mean signal amplitude of the normal group from that of the patient group during the ST segment and at the T-wave apex, and dividing the resulting amplitude difference by the corresponding standard deviation within all subjects. Results In MCG the optimal location for ST depression was at the right inferior grid for the RCA, at the mid-inferior grid for the LCX, and in the middle of these locations for the LAD subgroup (mean ST amplitudes: CAD −80 ± 360fT, controls 610 ± 660fT; p < 0.001). In BSPM it was on the left upper anterior thorax for the LAD, left lower anterior thorax for the RCA, and on the lower back for the LCX subgroup (mean ST amplitudes: CAD −39 ± 61 μV and controls 38 ± 38 μV; p < 0.001). In MCG the optimal site for T-wave amplitude decrease was the same as the one for the ST depression. In BSPM it was on the middle front for the LAD, on the back for the LCX and on the left abdominal area for the RCA group. In accordance with electromagnetic theory, the largest ST segment and T-wave amplitude changes took place in MCG in locations orthogonal to those in BSPM. Conclusion This study identified magnetocardiographic and BSPM recording locations which are sensitive for detecting transient myocardial ischemia by evaluation of the ST segment as well as the T-wave. These locations strongly depend on ischemic regions and are outside the conventional 12-lead ECG recording sites.

A 3-D model-based registration approach for the PET, MR and MCG cardiac data fusion

In this paper, a new approach is presented for the assessment of a 3-D anatomical and functional model of the heart including structural information from magnetic resonance imaging (MRI) and functional information from positron emission tomography (PET) and magnetocardiography (MCG). The method uses model-based co-registration of MR and PET images and marker-based registration for MRI and MCG. Model-based segmentation of MR anatomical images results in an individualized 3-D biventricular model of the heart including functional parameters from PET and MCG in an easily interpretable 3-D form.

Features of ST segment and T-wave in exercise-induced myocardial ischemia evaluated with multichannel magnetocardiography

BACKGROUND AND AIM. Magnetocardiography (MCG) is a novel, non-contact mapping technique to record cardiac magnetic field. We evaluated MCG criteria for myocardial ischemia in stress testing. METHODS. Multichannel MCG over frontal chest was performed in 44 patients with coronary artery disease (CAD) and 26 healthy controls during supine bicycle exercise test. Of the 44 patients 16 had anterior, 15 posterior, and 13 inferior ischemia documented by coronary angiography and exercise thallium scintigraphy. ST amplitude, ST slope, T-wave amplitude, and ST-T integral were measured. The optimal sites for detecting the ischemiainduced changes on MCG were sought. The orientation of the magnetic field was also determined. RESULTS. The optimal sites for the decrease of ST slope, ST amplitude, T-wave amplitude, and ST-T integral were over the abdomen. The reciprocal increase of these parameters was found over the left parasternal area. The optimal sites were approximately the same for all patient groups. In single-vessel disease patients without previous myocardial infarction (MI), ST slope increase and ST elevation performed the best (area under the receiver operating characteristic curve 92% and 90%, respectively). In post-MI patients with triple-vessel disease the decrease of T-wave amplitude and ST slope performed the best (area under curve 91%, for both). The magnetic field orientation at ST segment performed equally well as the other ST parameters. In stepwise logistic regression analysis, by use of the presence of CAD as the dependent parameter, ST slope increase and ST peak gradient orientation entered the model. CONCLUSIONS: Various ST segment and T-wave parameters detect ischemia in MCG. ST amplitude performs especially well in non-MI patients with less severe CAD. In advanced CAD late development of T-wave amplitude might be more sensitive to ischemia than ST amplitude.

Magnetocardiographic and Electrocardiographic Exercise Mapping in Healthy Subjects

AbstractIn 12-lead electrocardiography (ECG), detection of myocardial ischemia is based on ST-segment changes in exercise testing. Magnetocardiography (MCG) is a complementary method to the ECG for a noninvasive study of the electric activity of the heart. In the MCG, ST-segment changes due to stress have also been found in healthy subjects. To further study the normal response to exercise, we performed MCG mappings in 12 healthy volunteers during supine bicycle ergometry. We also recorded body surface potential mappings (BSPM) with 123 channels using the same protocol. In this paper we compare, for the first time, multichannel MCG recorded in bicycle exercise testing with BSPM over the whole thorax in middle-aged healthy subjects. We quantified changes induced by the exercise in the MCG and BSPM with parameters based on signal amplitude, and correlation between signal distributions at rest and after exercise. At the ST-segment and T-wave apex, the exercise induced a magnetic field component outward the precordium and the minimum value of the MCG signal over the mapped area was found to be amplified. The response to exercise was smaller in the BSPM than in the MCG. A negative component in the MCG signal at the repolarization period of the cardiac cycle should be considered as a normal response to exercise. Therefore, maximum ST-segment depression over the mapped area in the MCG may not be an eligible parameter when evaluating the presence of ischemia.

Heart rate adjustment of magnetic field map rotation in detection of myocardial ischemia in exercise magnetocardiography

Aims We studied the capability of heart rate (HR) adjusted change in multichannel magnetocardiogram (MCG) to detect exercise-induced ischemia. Methods and results The MCG and 12-lead ECG were recorded simultaneously during supine exercise testing in 17 healthy controls and 24 patients with single vessel coronary artery disease (CAD). In the MCG analysis, we plotted the orientation of the magnetic field map (MFM) against the HR in each cardiac cycle during recovery. A regression line was fitted to the data and the line slope (degrees/bpm) was determined. In the ECG, the ST-segment depression vs HR (ST/HR) slope was evaluated. The HR adjusted MFM rotation was more extensive in the pooled CAD group, and in all subgroups with different stenosed vessel, than in the control group at the ST-segment (1.5 ± 2.1°/bpm vs 0.29 ± 0.25°/bpm, p < 0.0005) and at the T-wave apex (0.95 ± 0.81°/bpm vs 0.24 ± 0.25°/bpm, p < 0.0005). Areas under the receiver operating characteristic curves of the HR adjusted MFM rotation at the ST-segment (88.5 %) and the T-wave (86.0 %) were higher than the ones without HR adjustment (75.5 % and 68.1 %, respectively), and higher than the area of ST/HR slope in the ECG (80.2 %). Conclusion HR adjusted MFM rotation detects transient ischemia independent of the stenosed vessel. HR adjustment improves the performance of the MCG in ischemia detection by the analysis of the ST-segment and the T-wave. The MCG was superior to the 12-lead ECG.

ST-segment level and slope in exercise-induced myocardial ischemia evaluated with body surface potential mapping.

Body surface potential mapping (BSPM) is superior to 12-lead electrocardiography for detection of acute and old myocardial infarctions (MIs). We used BSPM to examine electrocardiographic criteria for acute reversible myocardial ischemia. BSPM with 123 channels was performed in 45 patients with coronary artery disease (CAD) and 25 healthy controls during supine bicycle exercise testing. Of the 45 patients, 18 patients had anterior, 14 had posterior, and 13 had inferior ischemia documented by coronary angiography and thallium scintigraphy. The ST amplitude was measured 60 ms after the J-point and the ST slope calculated by fitting a regression line from the J-point to 60 ms after it. The optimal locations for detecting ST depression and ST-slope decrease were identified. In the pooled CAD patient group, the optimal location for ST depression was 5 cm below standard lead V(5) (CAD group: -70 +/- 70 microV; controls: 70 +/- 80 microV, p <0.001). Using a cut-off value of -10 microV, the ST depression separated the patients with CAD from controls with a sensitivity of 84% and a specificity of 96%. The ST slope became more horizontal in the patient group than in the control group. The optimal location for ST-slope decrease was over the left side (CAD group: 20 +/- 20 microV/s; controls: 720 +/- 320 microV/s, p <0.001). Using a cut-off value of 320 microV/s, the ST slope separated patients with CAD from controls with a sensitivity of 93% at a specificity level of 88%. The area under the receiver operating characteristic curve of ST slope tended to be higher than the one of ST depression (97% vs 93%; p = 0.097). In conclusion, regions sensitive for ST depression and for ST-slope decrease could be identified in BSPM, despite variation in the location of ischemia and the presence or absence of a history of MI. ST slope is a sensitive and specific marker of transient myocardial ischemia, and might perform even better than ST depression.

Beat-to-beat analysis method for magnetocardiographic recordings during interventions

Multichannel magnetocardiography (MCG) during exercise testing has been shown to detect myocardial ischaemia in patients with coronary artery disease. Previous studies on exercise MCG have focused on one or few time intervals during the recovery period and only a fragment of the data available has been utilized. We present a method for beat-to-beat analysis and parametrization of the MCG signal. The method can be used for studying and quantifying the changes induced in the MCG by interventions. We test the method with data recorded in bicycle exercise testing in healthy volunteers and patients with coronary artery disease. Information in all cardiac cycles recorded during the recovery period of exercise MCG testing is, for the first time, utilized in the signal analysis. Exercise-induced myocardial ischaemia was detected by heart rate adjustment of change in magnetic field map orientation. In addition to the ST segment, the T wave in the MCG was also found to provide information related to myocardial ischaemia. The method of analysis efficiently utilizes the spatial and temporal properties of multichannel MCG mapping, providing a new tool for detecting and quantifying fast phenomena during interventional MCG studies. The method can also be applied to an on-line analysis of MCG data.

Postmyocardial Infarction Patients Susceptible to Ventricular Tachycardia Show Increased T Wave Dispersion Independent of Delayed Ventricular Conduction

Arrhythmia Markers After Myocardial Infarction. Introduction: Experimentally, both delayed ventricular conduction and nonhomogeneous ventricular repolarization contribute to reentrant arrhythmias. We tested the hypothesis that increased T wave dispersion is independent of delayed ventricular conduction associated with arrhythmia vulnerability in postmyocardial infarction (post‐MI) patients.

Partial anomalous pulmonary venous return and atrial septal defect in adult patients detected with 128-slice multidetector computed tomography

The present series describes a group of adults with left-to-right shunts including partial anomalous pulmonary venous return (PAPVR) and/or an atrial septal defect (ASD) evaluated with ECG-gated 128-slice multidetector computed tomography (MDCT). PAPVR is defined as a left-to-right shunt where one or more, but not all, pulmonary veins drain into a systemic vein or the right atrium. PAPVR involving the right upper pulmonary vein can be associated with a sinus venosus ASD. The presence, course, number of anomalous veins and associated cardiovascular defects can be reliably observed by 128-slice MDCT angiography.

Magnetocardiographic indices of left ventricular hypertrophy.

Objective We tested the hypothesis that multichannel magnetocardiographic (MCG) mapping can detect and quantify the degree of left ventricular hypertrophy (LVH). Design A cross-sectional study. Setting Helsinki University Central Hospital, a tertiary referral center. Participants Forty-two patients with pressure overload induced LVH by gender-specific echocardiographic criteria (LVH group), and 12 healthy middle-aged controls. Main outcome measures MCG QRS-T area integrals and QRS-T angle in magnetic field maps in relation to echocardiographic LVH as well as left ventricular (LV) mass and structure. Conventional 12-lead electrocardiographic (ECG) LVH indices (Sokolow–Lyon voltage, Cornell voltage, Cornell voltage duration product) were assessed for comparison. Results MCG QRS- and T-wave integrals provided complementary information of echocardiographic LV mass. Their combination, the QRS-T integral, and the QRS-T angle were increased in patients with LVH and, in those patients, correlated significantly with LV mass indexed to body surface area (r = 0.455; P = 0.002 and r = 0.379; P = 0.013, respectively). A QRS-T integral > 16 000 fT⋅s had identical sensitivity of 62% at 92% specificity as the gender-adjusted Cornell voltage duration product of 240 μV⋅s for the detection of LVH. Conclusions The MCG method can detect patients with LVH and also quantify the degree of LVH in patients with increased LV mass.